1. Field of the Invention
The present invention relates to a novel extracorporeal circulation apparatus used when conducting a selective (or exclusive) cooling method employed in various medical treatments in mammals, especially in humans.
2. Description of the Related Art
Since Woodhall introduced in 1960 a systemic profound hypothermia under a cardiac arrest for the purpose of protecting a brain against a hemorrhage or an ischemia upon a craniotomy, the systemic profound hypothermia has been employed in many types of operations. However, a pump-oxygenator employed in this method makes the procedure complicated and the blood perfusion to various organs insufficient and the method requires a large amount of heparin as an anticoagulant, resulting in problems such as a secondary cerebral hemorrhage.
One of the inventors had made an effort to overcome the problems mentioned above and had developed a method for cooling a brain selectively (which is substantially similar in its meanings to the abovementioned xe2x80x9cselective cooling methodxe2x80x9d) while using a pump-oxygenator, and applied the method to a craniotomy (J. Neurosurg; Vol 24, pages 994 to 1001, 1966)). This selective cooling method did provide a cerebral hypotension safely but still involved problems with regard to the intra- and post-operative hemorrhages due to the use of a large amount of heparin still associated therewith.
In order to overcome these problems, one of the inventors discovered a method for injecting a cooled lactated Ringer""s solution into a cerebral artery to cool a brain exclusively and to dilute a blood simultaneously with the cooling of the blood, resulting in a substantially reduced heparin level, thereby reducing the risk of the hemorrhage (see Neurosurgery Vol 31, pages 1049 to 1055, 1992)). This method allows a reversible extreme hypotension to be established without undergoing an oxygen deficit and enables an extreme reduction in the amount of heparin to be used as a result of introduction of the cooled diluent, thereby allowing such an amount to be close to that used in an ordinary angiography. In addition, the introduction of the diluted blood into a lesion leads to various safety-improving effects such as reduction in blood loss.
As described above, by injecting the cooled lactated Ringer""s solution, a temperature of a brain is reduced. However, a volume of the lactated Ringer""s solution to be injected is generally large and therefore, the injection of the lactated Ringer""s solution allows the blood to be diluted excessively, thereby increasing a volume of circulating blood, which leads to humoral plethora, resulting in difficulty in maintaining the hypothermia for a sufficient period, due to which a satisfactory hypotension in the brain cannot be ensured. In addition, a large volume of the cooled diluted blood distributed throughout the entire body may cause problems such as reductions in body temperature and blood activity, a necessity for adjusting the blood electrolyte balance as well as an overhydration which is difficult to control only by a diuretic.
Accordingly, we have made an effort to solve the problems mentioned above, and finally discovered a novel extracorporeal circulation apparatus.
In a first aspect, the present invention provides an extracorporeal circulation apparatus used to perform the selective cooling method conveniently, and said apparatus comprises a diluent supply unit for cooling a diluent to a temperature below a body temperature and metering the diluent into a blood vessel, a blood concentration unit for metering diluted blood out from a blood vessel and concentrating the diluted blood thus drawn out to obtain a hematocrit value which is preferably at least 80% of the hematocrit value of the blood before dilution, and a blood supply unit for heating the concentrated blood to a temperature close to the body temperature and metering it into a blood vessel.
Accordingly, in a second aspect, the present invention resides in a method for applying the selective cooling method to a predetermined part (or a subject) of a mammal, especially of a human body, comprising, injecting a cooled diluent into a body at a site having an artery which is in direct or indirect communication with the part to be cooled, drawing a blood diluted with the diluent out from the body at a site having a vein which is in direct or indirect communication with said part, concentrating the diluted blood to recover blood in a state similar to that before the dilution, preferably blood substantially equivalent to the blood before the dilution, and, warming the recovered blood and then returning the warmed blood to the body at a venous site which is in direct or indirect communication with said vein and is closer to the heart.
Moreover, there is provided a method for treating a predetermined part of a mammal, especially of a human body, by means of applying the selective cooling method according to the second aspect to said part using the extracorporeal circulation apparatus according to the first aspect. Thus, in a third aspect, there is also provided a method for a treatment wherein the extracorporeal circulation method according to the second aspect is performed using the extracorporeal circulation device according to the first aspect, and the method includes a method for an operation and a method for controling a condition.
In the present invention, the term xe2x80x9cselective cooling methodxe2x80x9d means a method used in a medical field, especially in the field of a cerebral surgery, and means a method for selecting as a target part a part of a body, for example, an organ such as a brain, and then cooling said part locally. The selective cooling method is a locally cooling method used, for example, when a hemorrhage is predicted such as in a case of performing a surgical operation in a certain local region in a body (for example, the head), or when an operation is performed during a period in which a vital activity is reduced locally and transiently.